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The Spinning Balls That Steered a Steam Engine

8th grade nonfiction passage about the centrifugal governor: 268 words, six questions, an answer key and vocabulary.

8th grade nonfiction the centrifugal governor 268 words

The Spinning Balls That Steered a Steam Engine

Early steam engines suffered from a stubborn weakness, which was that their speed refused to stay constant. If the fire burned hotter, or if the machinery the engine was driving suddenly became easier to turn, the engine would race ahead. If the load grew heavier, it would slow down. A factory that depended on steady motion could not rely on a worker standing beside the engine all day, adjusting a valve by hand. Engineers wanted an engine capable of regulating itself.

An ingenious answer was the centrifugal governor, which James Watt used on his engines in the late eighteenth century. Picture a vertical shaft that is turned by the engine, with two heavy metal balls hanging from arms attached near the top. When the shaft spins slowly, the balls hang fairly close to it. When it spins faster, they swing outward and upward, because a spinning object tends to fly away from its center.

What matters is what the balls are connected to. A set of linked rods joins their arms to a throttle valve, the gate that controls how much steam reaches the engine. As the balls rise, the rods partly close the valve. Less steam flows in, and the engine slows down. If the engine slows too much, the balls sink, the rods open the valve again, and more steam rushes in.

The governor never needs a person to tell it what to do. The engine's own speed is the message, and the response pushes that speed back toward a steady value. Engineers call this feedback, and the same idea appears in thermostats and cruise control.

Questions

  1. What problem did early steam engines have? in the text

  2. What happens to the two balls when the shaft spins faster? in the text

  3. What does the throttle valve control? in the text

  4. What happens to the valve when the balls rise? in the text

  5. Why does the governor need no person to operate it? think about it

  6. Why is a thermostat described as using the same basic idea? think about it

Words to know

regulate
to control something so that it stays steady
centrifugal
describes the tendency to fly outward from a center
throttle
a valve that controls how much fuel or steam flows
feedback
using the result of a process to adjust that same process
shaft
a long rod that turns to carry power
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One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 211 words · Flesch-Kincaid grade 2.7

Early steam engines had a problem. Their speed did not stay the same. If the fire got hotter, the engine sped up. If the work got harder, the engine slowed down. A factory needs steady motion. It could not keep a worker beside the engine all day to turn a valve. Engineers wanted an engine that could control itself.

James Watt used a smart answer on his engines. It is called a centrifugal governor. A shaft stands up straight, and the engine turns it. Two heavy metal balls hang from arms near the top. When the shaft spins slowly, the balls hang close to it. When it spins fast, the balls swing out and up. A spinning thing tends to fly away from its center.

Rods link the balls to a throttle valve. The valve controls how much steam goes to the engine. When the balls rise, the rods close the valve a little. Less steam comes in, so the engine slows down. If the engine slows too much, the balls sink. The rods open the valve, and more steam rushes in.

No person has to tell the governor what to do. The engine's own speed is the message. Engineers call this feedback. Thermostats and cruise control use the same idea.

▲ This passage · 268 words · Flesch-Kincaid grade 7

Early steam engines suffered from a stubborn weakness, which was that their speed refused to stay constant. If the fire burned hotter, or if the machinery the engine was driving suddenly became easier to turn, the engine would race ahead. If the load grew heavier, it would slow down. A factory that depended on steady motion could not rely on a worker standing beside the engine all day, adjusting a valve by hand. Engineers wanted an engine capable of regulating itself.

An ingenious answer was the centrifugal governor, which James Watt used on his engines in the late eighteenth century. Picture a vertical shaft that is turned by the engine, with two heavy metal balls hanging from arms attached near the top. When the shaft spins slowly, the balls hang fairly close to it. When it spins faster, they swing outward and upward, because a spinning object tends to fly away from its center.

What matters is what the balls are connected to. A set of linked rods joins their arms to a throttle valve, the gate that controls how much steam reaches the engine. As the balls rise, the rods partly close the valve. Less steam flows in, and the engine slows down. If the engine slows too much, the balls sink, the rods open the valve again, and more steam rushes in.

The governor never needs a person to tell it what to do. The engine's own speed is the message, and the response pushes that speed back toward a steady value. Engineers call this feedback, and the same idea appears in thermostats and cruise control.

■ Harder · 296 words · Flesch-Kincaid grade 8.7

Early steam engines suffered from a stubborn and costly weakness, which was that their speed refused to remain constant. If the fire burned hotter, or if the machinery the engine was driving suddenly became easier to turn, the engine would race ahead of itself. If the load grew heavier, the engine would labor and slow down. A factory that depended on perfectly steady motion could not afford to keep a worker standing beside the engine all day, adjusting a valve by hand. Engineers therefore searched for an engine capable of regulating itself without human assistance.

An ingenious answer was the centrifugal governor, which James Watt used on his engines in the late eighteenth century. Picture a vertical shaft that is turned by the engine, with two heavy metal balls hanging from arms attached near the top of it. When the shaft spins slowly, the balls hang fairly close to it. When it spins faster, they swing outward and upward, because a spinning object tends to fly away from its center.

What makes the device remarkable is what the balls are connected to. A set of linked rods joins their arms to a throttle valve, the gate that determines how much steam is admitted to the engine. As the balls rise, the rods partly close the valve, so less steam flows in and the engine gradually slows. Should it slow too much, the balls sink, the rods open the valve again, and more steam rushes in to restore the pace.

The governor never needs a person to instruct it. The engine's own speed is the message, and the response pushes that speed back toward a steady value. Engineers call this principle feedback, and the same basic idea appears in thermostats, cruise control, and countless other modern machines.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put regulate, centrifugal, throttle, feedback and shaft on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 3 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 5 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "The Spinning Balls That Steered a Steam Engine"?

It was written for 8th grade. It has 268 words and works out to a Flesch-Kincaid grade level of about 7.0. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 4 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 3 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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